Timer for electric circuits



Oct. 28, 1930. A. R. JOHNSON TIMER FOR ELECTRIC CIRCUITS Filed Jan. 6,1928 [/v VENTOR firaen E. Job/250M I the length of time an electriccircuit is to be Patented Oct. 28, 1930 PATENT OFFICE ARDEN R. JOHNSON,OF ST. CHARLES, MISSOURI TIMER FOR ELECTRIC CIRCUITS Application filedJanuary 6, 1928.

This invention relates to timers for electric circuits, and particularlyto photographic print timers. It has for one of its ob ects providingmeans for automatically timing closed. The particular application of thetimer in this case is to the exposure of sensitized photographic sheetsto the light of an electric lamp. The invention has for a fur- 1O therobject providing means for enabling my invention Fig. 2 is an enlargedrear View of the apparatus with the rear side of the casing removed;Fig. 3 is a sectional new of the same along the line 3-3 of Fig. 2; andFig. 4: is an enlarged sectional view along 25 the line 44 of Fig. 3.

The operation of the timing apparatus which I provide depends primarilyon the swinging of a pendulum which, as 1t swings, closes and opens anelectric circuit and this, in turn,operates an electric light to whichthe sensitized photographic sheet is exposed. 13y suitable adjustments,the time during whlch the current is passed through the lamp can becontrolled, and the time of exposure thus can be made as little or asmuch as may be desired.

The apparatus, for convenience, is mounted in a casing 5 in the upperportion of which is a horizontally mounted supporting rod 6. To this rodis rotatably suspended a pendulum rod 7, and a pendulum bob 8 is fixedto the lower end of the rod. The length of the pendulum rod may bewhatever is convenient for the particular use, but I prefer, ordinarily,a rod which is about twelve inches long from its point of suspension tothe center of the pendulum bob; and the bob, in this instance, has adiameter of about two inches. However, it is to be understood that theseSerial No. 244,825.

dimensions are not an essential part of my invention.

The pendulum, as described, has a time of complete oscillation of aboutone second. Any convenient means may be provided for releasing thependulum and for stopping it after each complete oscillation has beenmade. I prefer, for the purpose, a pawl 10 which is pivoted to thependulum rod and which has a tooth 11 which is adapted to coact with apin 12 fixed to lever 13. This lever has its fulcrum 14 fixed to theside of the casing and it is resiliently held in the normal positionindicated by a spring 15. Fixed to the fulcrum 141, preferably on theoutside and on the front of the casing, is an operating arm 16. In orderto release the pendulum the operator presses downwardly on the arm 16, aflange 17 being provided for this purpose. This rotates the lever 18 soas to carry the lower end to the right and bring the inclined surface 20of the pawl against a projection 21, so that the pawl is forced upwardlywith reference to the pin 12 and is released from coaction with the pin.This releases the pendulum and allows it to oscillate. But, ordinarily,as soon as the pendulum is released, the operator releases the arm 16and the spring 15 forces the arm upwardly against a stop 28 and thelower end of the lever 13 is again brought back to normal position sothat the pawl 10 again coacts with the pin 12 as soon as the pendulumhas made a complete oscillation. Theinclined surface 20, coacting withthe pin 12, raises the pawl upwardly as the pendulum returns until thepin passes off from the surface and is caught by the tooth 11.

The lamp 54 is used, as hereinafter described, for printing thephotographs, and the means for controlling the light of the lampcomprise an electric circuit consisting of the wires 23 and 24. The wire23 passes to the lamp 54: in the ordinary manner and the wire 24 passesto any suitable source of electric supply 25 and thence, by the wire 26,to the lamp. The wire 23 is electrically connected to a switch terminal27 which is fixed toan arm 30. The arm 30 is rotatably mounted in anysuitable manner. In this instance,

V I prefer to suspend it rotatably on the rod 6.

contact with the terminal 27 and the lamp circuit will be closed. Asth earm 3Q is ro tatably mounted, when the" contact occurs the arm will becarried with the pendulum rod,

normally adjusted siti n, eeliersi e fier; described, and the contactbetween the terminals will be broken. Hence, the lamp Wlll be operatedonly during that portion ofthof complete oscillation that the two switchterminals are in contact In order to adjust the time of operation of thelamp, means are provided for varying. at will the position ofthe contact27. I pre:

. fer, for this purpose, an arm 32, also rotatably mounted on the rodGbutrigidiyfixed'to the arm 30 sov that the position of the arm 30 canbecontrolled by the positionoi the arm 32.

the casing. The arm 35 is fixedto a segmen-v tal member 36 which isrotatably; suspendedby the rod 6, or in any other suitablemanner.Obviously, byfvarying the position. of

the member 36, the position oi..tl1e.'ro d.3O and, hence, of. thecontact27, will be varied.

The lower edge ofLthe segmental member.

r and 31 will be relatively positioned sothat they will be in contactfor one second. during the swing of the pendulum. Or, if the pointerpoints to the line 41, the terminals will be in contactior half asecond. Hence, by

positioning the pointer with reference to the scale between the Zero11116 and theone.sec.

0nd line, the fraction of a second of time desired to operate thelampwill be obtained.

Ifit is desired -to operatethe' la'mp more than onesecond with theapparatus described herewith, the operator can hold the arm 16 down andthe'pendulum will then maketwo complete oscillations, or as manycomplete oscillations as may be desired. However, it severaloscillations are required, it may be necessary forthe operator t o'jrelejase the arm after two'or three oscillations sojwas to give thependulum an additional impulse. It will-be understood that in increasingthe length of time beyond one second; any addi- The arm 32crosse's aslot,33.in the cas ing. Passing through this slot. and. under; the arm32, thus suspending the arm, is a. fia nge34; fixed to another arm. 35'outsidexof' tional fraction of a second may be obtained by suitablyadjusting the position of the contact 27. For instance, if a second anda half is required, the pointer would be set for about, three-fourths ofasecond so that, during two oscillations, the total time that the lamp,would be operated wouldbe a second anjd a half a m Although there issome lag in the intensity ofthe light, after the closing of theterminals o ftliecircuit,whichaffects the effect of a the, light onthesensitized paper, yet, ordibut, on the return, the rod 30 'willstopatits narilytliisis compensated for by the lag in the dyingdownoithelight when the contacts are broken. s6 that, for ordinary lights atleast, this lagis immaterial,

The. particular application of myinv en-v tionin this case is to theprinting of photo.-

other reasons, and for this-purposeiI provide in, the casing an opening46 across whichlare, mounted strips of selected IlGgablVBSflQllllDI'lS:

ing, inthisinSfiaI Ce, strips 46, 47 and i8 The negative 48 is moredensethan the others and the, negative LT -is more so than the negative16; Back otthis opening, I place alamp. 50.

This lamp maybe supported in suitable I manner 5 for example, by meanjof abra cket 51, in the front of the openingj52 in the rear side of thecasing. Obviously, the; operator in iron; of. the caS ihgZwiIL Zbe. abletofobser ve.

the effect of the an the different. nega tives 1 6,- 4? and 4 8, andthefinteiisityfof the light will vary with reference to the relativedensities of the negatives.

Any sutable means may be usedior, exposing the sensitized puatst thelight when. the

timer is used for photographic:purposes; I prefer to use the followingdescribed 'ratus, Theprinting lamp Misenclosedia a, cas ng 53. Abovevthe printing lamp, is'

mounted a .trans aarent plate :55 on which is placedthe negative. 56'and the sensitized paper- 52, m any prdinary manner.

In determiningjthe time or exposure de sired, the operatorplaces thenegative on the platebfiand compares the {intensity or the light whichreaches his eye through thenegm tive with. the intensity of the lightpassing through the negatives 46, 1-? and d8, 'Ihee iposure necessaryfor a ,p articular negative showing ,a light intensity wh ch correspondstothelight intensity of one of thenegatives 46, 47 and48nvillbe the sameas the time experimentally, determined for that ,particu; lar negativei'For instance, ifthe time exp'erimentally determined for the particularnegaawisw e second,- and the lightintensit y through this negative, say48, corresponds to the negative undertest, the exposure of thesensitiiedsheetwould be,one sec-.

ond;- In this mannenthe operator can readily determine the approximatetime, and a little experience will indicate to him the exact timerequired for the exposure.

It will be obvious, that, having once set the apparatus for exposing adefinite length of time, as many prints may be taken as may be desiredwithout any resetting of the apparatus, as it is arranged to maintainany adjusted position indefinitely. For instance, although'the member 36is rotatably mounted in the rod 6, a spring 60 brings the segment firmlyagainst the wall of the casing but yields sufliciently to allow suitablerotation of the segment for a new adjustment. By means of the nut 61.,the compression of the spring may be made suiiiciently great to preventany misplacement of the segmental member by the operation of the deviceand, hence, when the apparatus is once set for a certain time, therewill be no change which would tend to vary the time of the exposure.

I claim as my invention:

1. A timer comprising a pendulum adapted to open and close an electriccircuit as it oscillates, means for oscillating said pendulum, saidmeans comprising a pawl pivoted to said pendulum, a pivoted arm, a pinfixed to said arm and adapted to coact with said pawl when the pendulumis rotated to one side of a vertical line passing through its point ofsupport, and means for releasing said pawl from coaction with said pin.

2. A timer comprising a pendulum adapted to open and close an electriccircuit as it oscillates, means for oscillating said pendulum, saidmeans comprising a pawl pivoted to said pendulum, a pivoted arm, a pinfixed to said arm and adapted to coact with said pawl when the pendulumis rotated to one side of a vertical line passing through its point ofsupport, and means for releasing said pawl from coaction with said pin,said releasing means comprising means for moving said pin further awayfrom said line, and means for releasing said pawl from said pin.

In testimony whereof, I hereunto set my hand.

ARDEN R. JOHNSON.

